Simulation of in-pile irradiation effects in nickel and austenitic steels by bombardment with intermediate energy Ni+ ions

The main interest of heavy ion bombardment is to produce a significant number of atomic displacements very quickly, within a few hours, which would take at least a year of irradiation in a reactor. However, this technique has drawbacks: low penetration of heavy ions, non-homogeneous defect production, and implantation of foreign atoms into the sample. We studied the formation of cavities by agglomeration of vacancies (swelling) in nickel bombarded by Ni+ ions at 500 keV. The swelling varies with temperature and reaches a maximum around 620 °C. Pre-loading with helium increases the number of cavities but decreases the swelling. The swelling increases linearly with fluence. The number and size of cavities increase rapidly at the beginning of irradiation. We investigated the evolution of dislocation density in an austenitic steel bombarded by Ni+ ions. We observed a high dislocation density between 400 and 700 °C. This density is independent of the initial state of the material (overheated or work-hardened) and of the fluence once it reaches a value close to 10 displacements per atom. It increases with flux and decreases as temperature rises.